The stable, concentrated, basic dye solutions of this invention are unknown in the art.
Basic azomethine dyes are used extensively in the form of relatively dilute aqueous solutions in the paper, textile and leather industries. Heretofore, dyeing solutions have been prepared by the dyer from finely ground dyes. The finely ground dyes have the disadvantage of caking through the action of moisture or heat, with subsequent difficulty in dissolving the dyes. Moreover, weighing or transferring the powdered dyes is attended by unpleasant dust formation. In addition, during dissolution of the dyes and subsequent stirring, frothing often takes place leading to consequent contamination and loss.
Use of the stable, concentrated dye solutions of this invention will insure a more uniform dye bath strength. Also, the highly concentrated solution can be fed into the dye bath by a simple metering process.
The novel process has several advantages over prior art processes. The novel process leads to pure dyes that are substantially free of unreacted azo dye base and/or protonated dye salt contamination caused, inter alia, by not using acid-binding agents or by not using them in sufficient amount. Because of this freedom from azo dye base and protonated dye salt contamination, the dyes produce brighter dyeings having very good light fastness and sublimation fastness compared to dyeings made with contaminated dyes.
Further, the novel process leads to dyes substantially free of the water-insoluble carbinol form of the dye which requires an additional acid neutralization step to be converted to the desired quaternized form. The carbinol form sometimes results from alkaline neutralization of the quaternized dye salt during quaternization when an alkaline acid-binding agent is employed. Detectable amounts of the carbinol form in the final dye will of course, cut down correspondingly on dye strength and adversely affect the shade. A lowering of yield will also occur.